Amazed that anyone expects parents of 11yr olds to stay. Here parents stay for parties until about half way through reception. Beyond that it is up to the host to ask a few friends etc to help with crowd control. We do have class lists, which are voluntary, and organised by class reps so not coming from the school. I always bring that to the party, but most parents don't dd2 is a bit sensitive but determined to go solo, so I do tend to leave our phone number, because as her parent I would hate her to be upset for an hour and for me to be uncontactable, she never has needed me and is much more confident now.
YANBU though to expect the boys to behave. They were probably fired up by the activity, but even so their behaviour must have been exceptional for the party venue to comment. That would be a good reason to have the parent's number, I would be furious with my dc if one of them behaved like that and would happily collect them, but would be a bit uncertain about leaving them with you again if I thought you couldn't cope. My dc are generally well behaved, but children do smell fear so maybe they thought they could take advantage.
scottishmummy if your eldest dc is only in P1, do ask some parents with older children in your school when drop offs begin so you don't get a shock at the next party you organise. If I based my knowledge of party organisation on my experience of the first term or so of reception I would assume parents always attended. By February when my girls have birthdays only about half the parents stay, by year 1 here you only stay if your child is particularly shy or has additional needs.
I actually prefer the parents not to stay, except those specifically asked, as they generally expect drinks etc when I am wanting to entertain their children, and they chat loudly when I want all the dc to be quiet and listen to my instructions. It would be a nighmare as a teacher if you always had loads of parents sitting in the corner of your classroom chatting and having to offer them tea and coffee while trying to make sure their children had lots of fun activities.
It is different though when they are v little, I don't want to worry about taking the to the loo etc, or them in tears in the corner because they didn't win the middle of pass the parcel. But then the parties are different and you can't expect little children to join in in the same way.